In fractionating towers and other fluid contact vessels, it is customary to provide manways in the trays thereof (one for each flow path of each tray) so as to permit the passage of workmen, tools, tray plates and supports therefor as well as other equipment from one tray to another. Each manway comprises an opening, usually quadrangular, in each tray and an overlying complementary cover or closure of slightly greater dimensions than the opening so as to overlap the marginal edge portions of said tray contiguous said opening and rest on the manway frame forming the margins of the latter. Preferably, suitable fasteners, such as frictional clamps, detachably connect the cover or closure of each manway to its tray in overlying relation to the opening of the manway and are operable from above and below the tray whereby one workman may open and close said manway from thereabove and/or therebelow without assistance. Heretofore, the dimensions of a manway have been limited to a degree by the distance between adjacent trays due to the necessity of the closure or cover being slightly larger than the opening of said manway and still permit passage of said closure through said opening.
Since it is not economical to provide a manhole in the wall of a fractionating tower or other fluid contact vessel for each tray, it is frequently necessary to pass a manway cover or closure as well as other articles and tray parts through its opening as well as the manway openings of other trays. Also, the size of the vessel manhole limits the width or lesser dimension of the manway closure as well as of the tray plates and supports therefor. In addition, the installation and removal of a conventional manway closure is time consuming since it is necessary to frictionally clamp or otherwise detachably fasten all of the margins of the closure to the underlying marginal edge portions of the tray. Another factor that must be taken into consideration is that each manway cover or closure must conform to the structure of its tray so that it does not materially affect the overall characteristics and/or performance of the tray. Difficulty is also encountered when the diameter of the tower or vessel is relatively small as well as when the space between adjacent trays is obstructed, such as by downcomers. Frequently, a manway may be of less transverse dimension in one direction, such as width, than in the other direction or length since an oblong or elongate manway accommodates the passage of a workman, tools, tray parts and most other equipment which generally have an oblong configuration.
The space between adjacent fluid contact trays may be between 12 and 48 inches, but ordinarily is from 12 to 24 inches. Although the external diameter or maximum transverse dimension of the manholes in the wall of a fluid contact vessel may vary from 16 to 24 inches, usually, said external diameter is between 16 to 18 inches. Accordingly, conventional tray manways have a maximum width or lesser dimension of from 11 to 15 inches. It is noted that the perimetrical shape of the manway is not critical, since it may be of any suitable polygonal configuration, such as triangular, quadrangular, hexagonal, trapezoidal, parallelogram, etc. Normally, rectangular configuration best lends itself to the angular relationship of the margins of tray plates and supports therefor. For economy of manufacture as well as installation and removal, trays of the same or similar type in a fluid contact vessel are as uniform as possible and have generally identical manways in the same relative position. Additionally, the shape, size and location of the manway of a tray may be controlled by the structure of adjacent trays and/or their manways.